And after the movie during the credits, they show some of the training that was done for the movie - from the looks of it, kinda looks like an MMA gym, they had a ring where they were practicing throws and grappling, bagwork, and thai pad work.

Not a bad blend of MMA and hong kong movie kung fu.

I've got a copy of the HK two disk set which has a couple of nice features about the training and martial arts used in the film. One of the features is named 'ultimate fighters' and is an extended version of stuff you see in the credits with Donnie talking over the top (in English) about MMA, training, and getting it to look both good and real in the film.
There's a nice long Making Of also which features more gym training, but also Donnie and his action crew on set going through and working out the moves. Well worth a look as there are moves that aren't in the movie, and different angles to some that are. Also cast members talking about how much it all hurt to film. :)

It was freaking cool. I just got the CD 2 days ago. It was really MMA with lots of HK style action movie thrown in for flavor. Hong Kong action movie of our generation. If my guess is right, we'll be seeing this become more mainstream.